Iron is one of the first crafted materials the player will create in the game. It is a required material in the production of Construction Parts and Mechanical Parts, making it one of the highest-demand items in the early stage of the game. But, from the mid-stage, the demand for iron is partially replaced by Steel, and one for iron will be stagnant.
Below are all the recipes, which contain this item. Note, that some of them may be locked behind Research, and not immediately available in your game.